Gene Study Links Snakes to Land Lizards
New genetic evidence may solve the long-running dispute over whether snakes evolved from lizards in the ocean or lizards on land. The latest evidence comes down firmly on the side of land.
Both sides of the argument have generally agreed that that leap occurred about 150 million years ago, but they have not agreed on where it happened.
Recent fossil finds of sea-going snakes with small rear legs had tipped the debate in favor of the ocean, with many researchers believing that snakes evolved from mosasaurs, the only lizards living in the ocean when snakes emerged.
The new data pushes the debate back the other way.
Biologists Nicholas Vidal and S. Blair Hedges of Pennsylvania State University collected the DNA for two genes from 64 species representing all 19 families of living lizards and 17 of the 25 families of living snakes.
Genetic material from some of the lizards was difficult to obtain because the reptiles live in remote areas. But, Hedges said, “we felt it was important to analyze genes from all the lizard groups, because almost every lizard family has been suggested as being the one most closely related to snakes.”
The two genes perform the same functions in all the species tested, but they have slightly different DNA blueprints because of evolution. Vidal and Hedges used well-known techniques comparing those differences to produce a family tree showing how the species are related.
They report in an upcoming issue of the journal Biology Letters that snakes are only distantly related to the giant Komodo dragon, the closest living relative of the mosasaurs. Had snakes evolved from mosasaurs, they would have been most closely linked to the dragons.
The new evidence also suggests that snakes lost their limbs as they descended from lizards that burrowed underground in search of prey. “Having limbs is a real problem if you need to fit through small openings underground,” Hedges said. “Your body could fit through much smaller openings if you did not have the wide shoulders and pelvis that support your limbs.”
